This invention relates to structural members, such as box beams, for building structures. More particularly, it relates to structural members constituted of interlocked components (e.g. channel sections or the like), and to interlocking elements therefor.
In U.S. Pat. No. 3,382,639, there is described a box beam construction comprising two identically dimensional, elongated, extruded rigid channel sections arranged with their channels opening toward each other and the longitudinal edges of their legs in abutting alignment to constitute joints between the channel sections. The inner surface of each channel leg, adjacent its edge, bears a longitudinal finger or lip projecting inwardly to define a generally V-shaped recess opening in the same direction as the channel, with a retaining shoulder formed along the free edge of the lip; thus, at each joint, there are two such recesses (i.e. one on each of the channel section legs that meet at the joint) opening toward each other across the joint. The channel sections are interlocked at the joints by means of elongated splines inserted in the recesses, each spline including a web portion bridging the joint inwardly of the channel section legs and a pair of spline legs extending inwardly from opposite sides of the spline web for respectively engaging the lips of the two recesses adjacent the joint behind their shoulders. It will be understood that terms such as "inner" or "inwardly," and "outer" or "outwardly," as used herein, refer respectively to directions toward and away from the interior of the box beam or other hollow structural member.
As an example of use of the described beams, the above-cited patent shows a screenroom enclosure wherein the beams serve as vertical wall posts and horizontal ceiling beams in a framework for supporting screen cloth panels stretched between the beams. The edges of the screen cloth panels are received in outwardly-opening longitudinal pockets formed in the channel sections that make up the beams, and are held in place by elongated plastic splines inserted in the pockets. Each beam at a corner of a wall or ceiling supports edges of two screen cloth panels lying in planes perpendicular to each other, while each of the other beams in the assembly supports edges of two screen cloth panels lying in a common plane.
A beam of the foregoing type is typically assembled by first inserting one side of one of the interlocking splines into a recess on one leg of a first one of the constituent channel sections, similarly inserting one side of the other spline into the other recess (i.e. on the other leg) of the same channel section, fitting the two recesses of the other channel section over the exposed sides of the two splines, and pressing the two channel sections together. With the known form of these elements, however, this assembly procedure has tended to force the splines so deeply into the recesses of the first channel section as to prevent proper engagement of the spline legs behind the shoulders of the lips of the second channel section. To avoid this difficulty, it has heretofore been necessary to manufacture the splines and channel sections to inconveniently and uneconomically close tolerances. A further problem encountered with the known design is that two specifically different channel sections (respectively having the screen-cloth-receiving pockets at different positions on their exteriors) have had to be produced for the corner posts and beams of a screen enclosure, in order properly to locate the screen cloth panels relative thereto.